The United States Postal Service (hereafter referred to as the USPS) has implemented a program known as the Information Based Indicia Program (IBIP) which permits a user to generate a particular type of a postage indicium for sending a mail piece (e.g., letter, package, etc.). Typically, the user employs a postage meter certified by the USPS (or the government or private postal service for another country) to generate the indicium. The IBIP provides certain standards and regulations that the user must follow to purchase and print the indicium. For example, the IBIP specifies that the indicium must contain certain required information and may contain certain optional information such as, without limitation, the paid postage amount, the date and time the indicium was generated, the identification number of the postage meter used to generate the indicium, a postal service symbol, the class of service desired for the mail piece, the addressee ZIP code and/or address, and the sender's name and/or address.
The IBIP generally requires that the postage indicium be comprised of machine readable and human readable portions. The machine readable portion of the indicium may be in the form of a two dimensional barcode, such as, without limitation, a Data Matrix symbol. As is known, each Data Matrix symbol consists of a number of data regions having nominally square barcode modules arranged in an array. Each barcode module generally represents one bit of data. For a black on white Data Matrix symbol, for instance, a darkened (i.e., filled) barcode module represents a binary “one” and a light (e.g., empty or white) barcode module represents a binary “zero”. The data regions are usually surrounded by a finder pattern which, in turn, is surrounded by a quiet zone border. Multiple data regions may be separated by an alignment pattern. A detailed description of the Data Matrix symbology can be found in ISO/IEC International Standard 16022:2000(E) entitled “Information Technology—International Symbology Specification—Data Matrix”.
The Data Matrix symbol in an IBIP indicium may carry encrypted information, such as the postage amount and other postal data that relate to the mail piece and to the postage meter that printed the indicium. The encrypted information which is in the symbol is usually referred to as a digital token or a digital signature, and it is used for authentication purposes. The encryption is also used to protect the integrity of information, including the postage amount, imprinted on the mail piece for later verification of postage payment. As a result, the altering of the printed information in an indicium, such as information relating to evidence of postage payment, is detectable by standard digital signature verification or Message Authentication Code (MAC) procedures. Examples of systems that are capable of generating and printing such indicia are described in U.S. Pat. Nos. 4,725,718, 4,757,537, 4,775,246 and 4,873,645, each assigned to the assignee of the present invention.
After indicium information and a barcode symbol representing the indicium information are generated, the indicium is either printed directly onto a mail piece or onto a meter tape or label that is attached to a mail piece. The mail piece is then deposited with the USPS where the indicium may later be verified. For example, the USPS may use an optical scanning device to create a digital image of the indicium. A barcode reading routine may then be employed to verify the authenticity and data integrity of the indicium (e.g., by decoding and interpreting the information contained within the indicium).
In order for the optical scanning device and barcode reading routine to function properly, it is critical that the print quality of postage indicia be at least at a certain acceptable level. This is especially true for Data Matrix symbols that employ barcode modules having a small size. For example, distortions (i.e., incorrect vertical or horizontal alignment of the modules within the symbol) and defects (e.g., streaks, lines, etc. running through the symbol) in the matrix grid may cause problems for the optical scanning device and/or the barcode reading routine. Defects and distortions may cause the reading system to fail to properly read the barcode, which can cause a verification failure of otherwise perfectly legitimate IBIP symbols. The mail piece may be incorrectly rejected as having inadequate postage and the requested level of service (e.g., first class) may not be provided as a result of a defect or distortion present in the matrix grid.
Thus, there exists a need for a system that generates barcodes in which information encoded within a two-dimensional barcode is easier to read.